More than 400 years ago, Giordano Bruno, an Italian monk, wrote that
"In space there are numberless earths circling around other suns,
which may bear upon them creatures similar or even superior to those
upon our human Earth."

Bruno deserves to be remembered in the
millennium year - he was burnt at the stake, in Rome, in the year
1600.

In the late 19th century, the science fiction of Jules Verne and
H.G.
Wells popularized the idea of alien life. Percival Lowell, a wealthy
American, built his own observatory in Flagstaff, Arizona primarily
to study Mars.

He believed that its surface was criss-crossed by
'canals', dug by an advanced civilization to channel water from the
frozen polar caps to the 'deserts' near the Red Planet's equator.

In 1900, a French foundation offered the Guzman Prize of 100,000
francs for the first contact with an extra-terrestrial species; but
prudence led them to exclude Mars - detecting Martians was then
thought to be too easy!

NASA

Is there life on Mars
- the idea has always fascinated us.

How life began, and whether it exists
elsewhere remains one of the most fascinating questions in the whole
of science - indeed, you don't need to be a scientist to wonder
about this.

But we still don't know the answer. We're less
optimistic about Mars than our forbears were a hundred years ago.
Even if there is life there, it would be nothing more than
microscopic 'bugs' of the kind that existed on Earth early in its
history - there is certainly nothing on Mars like the 'Martians' of
popular fictions.

Indeed, nobody now expects 'advanced life' on any of the planets or
moons in our Solar System.

But our Sun is just one star among
billions. And in the vastness of space far beyond our own Solar
System we can rule out nothing. Astronomers have discovered, just
within the last five years, that many stars have their own retinue
of planets. There are millions of other Solar Systems.

And there
would surely, among this vast number, be many planets resembling our
Earth.

Lynette Cook

Life could be
everywhere;

over 31 planetary systems have been discovered around
other suns

If intelligent aliens were common,
shouldnít they have visited us already?

Some people, of course,
claim that aliens have indeed visited us. But the evidence for UFOs
is no better than that for ghosts, and I'm personally quite
unconvinced.

Some astronomers cite this as evidence that aliens are
rare. They note that some stars are billions of years older than our
Sun, and point out that, if life were common, its emergence should
have had a 'head start' on planets around these ancient stars.

But the fact that we haven't been visited doesn't, in my view, imply
that aliens don't exist - the question remains open. It would be
far harder to traverse the mind-boggling distances of interstellar
space than to send a radio signal. That's perhaps how aliens would
reveal themselves first.

The nearest stars are so far away that
signals would take many years in transit. For this reason alone it
makes sense to 'listen' rather than transmit - if a signal were
detected, there would be time to send a measured response, but no
scope for quick repartee!

(Aliens equipped with large radio
antennae could in any case pick up the combined output of all our TV
transmitters - if they could decode them, it's hard to think what
they might conclude about 'intelligent' life on Earth!).

Seth Shostak

ET please phone Earth
- SETI listens for radio signals from

alien civilizations
at the Arecibo Radio Telescope

Attempts to search for such signals have
had a hard time getting public funding (even at the level of the tax
revenues from a single science fiction movie) because the topic is
encumbered by 'flakey' associations with UFOs, and so forth.

But
thereís a serious effort in California, backed by hefty donations
from some silicon-valley millionaires.

We have no idea what intelligent aliens would look like - it would
depend on the habitat that their 'home planet' offered. They could
be balloon-like creatures floating in dense atmospheres; they could
be the size of insects, on a big planet where gravity pulled
strongly. Or they may be freely-floating is space.

They could even,
as some science fiction reminds us, be super-intelligent computers,
created by a race of alien beings that had already died out.

Even if intelligent aliens existed, they may not be transmitting any
signals; and their brains and senses may be so different from ours
that we couldn't recognize them. There may be a lot more life out
there than we could ever detect - absence of evidence wouldn't be
evidence of absence. There are heavy odds against such searches
succeeding.

But I'm enthusiastic about these searches, because of the import of
any manifestly artificial signal. Even if we couldn't make much
sense of it, we'd have learnt that 'intelligence' wasn't unique and
had emerged elsewhere.

Our cosmos would seem far more interesting;
we would look at a distant star with renewed interest if we knew it
was another Sun, shining on a world as intricate and complex as our
own.

NASA

Galaxies, stars and
planets, a cosmic structure we share with any aliens

If we ever established contact with
aliens, what could we discuss with them?

I've argued in a new book
that we're assured one common interest. We'd belong to the same
universe of stars and planets, all made of similar atoms and
governed by universal laws. We'd all trace our origins back to a
single 'genesis event' - the so-called 'big bang', which happened
about 12 billion years ago.

To firm up the odds on alien life, we need to understand how life
begins and evolves. An extraordinary precession of species (almost
all now extinct) have swum, crawled and flown during the Earthís 4.5
billion year history.

For a billion years, primitive 'bugs' exhaled
oxygen, transforming the young Earth's poisonous atmosphere and
clearing the way for our eventual emergence.

We know from fossils that a cornucopia
of swimming and creeping things evolved during the Cambrian era 550
million years ago. The next 200 million years saw the greening of
the land, offering a habitat for exotic creatures - dragonflies as
big as seagulls, millipedes a yard long, giant scorpions and
squid-like sea-monsters.

Then came the dinosaurs. Their sudden
demise opened the way to mammals - to the evolution of apes and us.
We are the outcome of time and chance: if evolution was 're-run',
there would be no humans, and we can't predict whether any other
species would achieve our dominant role.

So we can't lay firm odds on whether
'intelligence' would emerge on another Earth-like planet.

NASA

Is there life under
the icy crust of Europa?

We know this happened on Earth, but we'd
dearly like to discover a second example where even the earliest
stages of life might exist.

Mars remains the best place to look.
Three years ago, American scientists announced evidence for fossil
'bugs' on a meteorite that had come from Mars. This claim, hyped up
at a press conference attended by President Clinton himself, was
dubious and premature - NASA has been backtracking on it ever
since.

We'll learn more from a series of space
probes that will be sent to Mars in the next decade, to study its
surface, and eventually return samples to Earth. And there are
longer-term plans to search elsewhere - for instance, a submersible
robot will probe the ice-covered oceans of
Jupiter's moons Europa
and Callisto.

All this depends on the space program.

For most of the present
century, space travel was a futuristic concept, familiar from comics
and corn flakes packets. But in July 1969, Neil Armstrong's 'one
small step' made space travel a reality. Those of us who are now
middle-aged can remember viewing 'live' the murky TV pictures of
that event: it seemed a high point in a decade blighted by the arms
race and the Vietnam war.

Another lasting image from the 1960s was the first photograph of the
entire round Earth, taken from the Moon. Our habitat of land, oceans
and clouds was revealed as a thin delicate-seeming glaze. Our home
planet - the 'third rock from the Sun' - is very special.

The
beauty and vulnerability of 'spaceship Earth' contrasts with the
stark and sterile moonscape on which the astronauts left their
footprints.

NASA
Neil Armstrong's giant leap for mankind was fuelled by the Cold War.

In the 1960s, the first brief excursions
to the Moon seemed just a beginning.

We imagined follow-up projects:
a permanent 'lunar base', rather like the one at the South Pole; or
even huge 'space hotels' orbiting the Earth. Manned expeditions to
Mars seemed a natural next step. But none of these has happened. The
year 2001 will not resemble Arthur C. Clarke's depiction, any more
than 1984 (fortunately) resembled Orwell's.

The program, announced by President Kennedy in 1961, 'to land a
man on the Moon before the end of the decade, and return him safely
to earth', was lavishly funded because America wanted to beat
Russia. Their pride had been badly dented in 1957, when Russia
launched the first 'Sputnik', and this was a chance to recapture the
lead in the space race.

Reaching the Moon was an end in itself: the
last lunar landing was in 1972.

Manned spaceflight now seems a rather jaded spectator-sport: the
veteran senator John Glenn's recent trip in the Space Shuttle may
have been a morale-booster for elderly Americans, but it didn't
recapture the excitement of his pioneering flight 36 years earlier.
We admired the Russian cosmonauts more for their fortitude and DIY
skills than for anything else, as they coped with one malfunction
after another in the decrepit Mir spacecraft.

Nationals of other countries have hitched rides into space. The
British astronaut Michael Foal heroically survived the hazards of
Mir, the Russian Space Station. French, Bulgarian and Mongolian
astronauts have also made the trip.

But none of this has recaptured
public enthusiasm.

NASA
Perhaps the best astronauts are robots

The practical case for manned
spaceflight was never strong, and it gets weaker as robots and
computers get more powerful.

Space technology - now funded
commercially as well as by governments - has abundantly proved its
value. Thousands of small unmanned objects have been launched into
orbit.

Satellites are routinely used for long distance telephones and
satellite TV broadcasts. The 'global positioning satellites' allow
planes or ships to navigate precisely - and allow solo hikers or
sailor to locate themselves accurately anywhere on Earth, with a
pocket-sized instrument. Weather forecasts depend on pictures and
data from space.

Space exploration need not involve humans. It can be better (and far
more cheaply) carried out by fleets of unmanned probes, exploiting
the advances that have given us mobile phones and high-powered
personal computers.

Cameras and scientific instruments have beamed back pictures from
the other planets of our Solar system. And the Hubble Space
Telescope has imaged stars and galaxies so deep in space that their
light set out on its journey towards us billions of years before our
Earth and Sun were born.

The cosmos is fantastically larger and more
complex than could have been imagined by the ancients who first
mapped the constellations.

The cosmos confronted with huge spans of time, as well as stupendous
expanses of space. Life on Earth has evolved for billions of years,
but our Sun has burnt up less than half its fuel, and will keep
shining for another five billion years. If life isn't prematurely
snuffed out, our remote progeny will surely - in the aeons that lie
ahead - spread far beyond this planet.

We plainly can't forecast the vastly remote future. But what might
happen in the first decades of the new millennium? How long will it
be before people return to the Moon, and perhaps explore still
further afield?

NASA
Worth its weight in gold - a section of the International Space
Station

The centerpiece of the current US
program is the new International Space Station: this will be in
orbit a few hundred miles up, and the size of a football field.

It
will be the most expensive artifact ever constructed, costing its
own weight in gold. Even if it is finished - something that seems
uncertain, given the immense and ever-rising costs, and prolonged
delays - it will be neither practical nor inspiring.

Thirty years
after men walked on the Moon, a new generation of astronauts will be
going round and round the Earth, in more comfort than Mir can offer,
but much more expensively. The astronauts will be
able to do experiments, but most of those could be done more cheaply
by robots in smaller free-flying satellites.

The Space Station would make somewhat more sense as a staging post
on the way to other planets. But no such follow-up will materialize
unless public enthusiasm revives, or unless some technical
breakthrough renders space travel much cheaper and easier than it
now seems.

Present launching techniques are as extravagant as air travel would
be if the plane had to be rebuilt after every flight. Spaceflight
will only be affordable when it adopts the same techniques as
supersonic aircraft. Tourist trips into orbit may then become
routine. And wealthy adventurers may boldly go further. Future
Richard Bransons, for whom round-the-world ballooning seems too tame
and routine, could aim for the Moon.

If Bill Gates seeks a challenge that
won't make his later life seem an anticlimax, he could sponsor the
first expedition to Mars.

NASA
Armageddon? - an asteroid impact on Earth

Some people use the so-called 'insurance
policy argument' to advocate a manned space program.

There is an
ever-present risk (though fortunately a small one) that a comet or
asteroid will hit the Earth. The craters on the Moon's surface are
records of these impacts. An impact on Earth - leaving a huge
undersea crater near Chicxulub in the Gulf of Mexico, probably
sealed the fate of the dinosaurs 65 million years ago.

There is about one chance in 10000 that, within the next 50 years,
the Earth will be hit by an asteroid large enough to cause
world-wide devastation - ocean waves hundreds of feet high,
tremendous earthquakes, and changes in global weather. This chance
is low - but no lower than the risk (for the average person) of
being killed in an air crash. Indeed, it's higher than any other
natural hazards that most Europeans or North Americans are exposed
to.

The ever-present risk from nature has been augmented since humankind
entered the nuclear and biotechnological age. Humanity will remain
vulnerable to these (probably increasing) hazards so long as it is
confined here on Earth.

But once self-sustaining communities exist
away from the Earth - on the Moon, on Mars, or freely floating in
space - our species would be invulnerable to any global disaster,
and whatever potential it has for the 5-billion-year future could
not be snuffed out.

Whether on not humans spread beyond the Earth during the next
millennium, we'll still want to know whether we are alone. It would
in some ways be disappointing if searches for alien intelligence
were doomed to fail. On the other hand, it would boost our 'cosmic'
self-esteem. If our tiny Earth were a unique abode of intelligence,
we could view it in a less humble cosmic perspective than it would
merit if the Galaxy already teemed with complex life.

We'd have even
stronger motives to cherish this 'pale blue dot' in the cosmos, and
not foreclose life's future - a future that could be even longer
than the time span over which simple life has evolved into humans.

That is why we should expand our cosmic
vision in the new millennium.

Today, most scientists are convinced that we are not alone. But what
life exists in our own back yard Ė our Solar System?

Just do the numbers: Several
hundred billion stars in our galaxy, hundreds of billions of
galaxies in the observable universe, and 150 planets spied already
in the immediate neighborhood of the sun.

That should make for
plenty of warm, scummy little ponds where life could come together
to begin billions of years of evolution toward technology-wielding
creatures like ourselves. No, the really big question is when, if
ever, we'll have the technological wherewithal to reach out and
touch such intelligence. With a bit of luck, it could be in the next
25 years.

Workers in the search for extraterrestrial intelligence (SETI) would
have needed more than a little luck in the first 45 years of the
modern hunt for like-minded colleagues out there.

Radio astronomer
Frank Drake's landmark
Project Ozma was certainly a triumph of hope
over daunting odds. In 1960, Drake pointed a 26-meter radio
telescope dish in Green Bank, West Virginia, at two stars for a few
days each. Given the vacuum-tube technology of the time, he could
scan across 0.4 megahertz of the microwave spectrum one channel at a
time.

Almost 45 years later, the SETI Institute in Mountain View,
California, completed its 10-year-long
Project Phoenix.

Often using
the 350-meter antenna at Arecibo, Puerto Rico, Phoenix researchers
searched 710 star systems at 28 million channels simultaneously
across an 1800-megahertz range. All in all, the Phoenix search was
100 trillion times more effective than Ozma was.

Besides stunning advances in search power, the first 45 years of
modern SETI have also seen a diversification of search strategies.
The Search for Extraterrestrial Radio Emissions from Nearby
Developed Intelligent Populations (SERENDIP) has scanned billions of
radio sources in the Milky Way by piggybacking receivers on antennas
in use by observational astronomers, including Arecibo.

And other
groups are turning modest-sized optical telescopes to searching for
nanosecond flashes from alien lasers.

Listening for E.T.

The SETI Institute is deploying an array of
antennas and tying them into a giant "virtual telescope."
CREDIT: SETI

Still, nothing has been heard. But then, Phoenix, for example,
scanned just one or two nearby sunlike stars out of each 100 million
stars out there.

For such sparse sampling to work, advanced,
broadcasting civilizations would have to be abundant, or searchers
would have to get very lucky.

To find the needle in a galaxy-size haystack, SETI workers are
counting on the consistently exponential growth of computing power
to continue for another couple of decades. In northern California,
the SETI Institute has already begun constructing an array composed
of individual 6-meter antennas.

Ever-cheaper computer power will
eventually tie 350 such antennas into "virtual telescopes," allowing
scientists to search many targets at once.

If Moore's law - that the
cost of computation halves every 18 months - holds for another 15
years or so, SETI workers plan to use this antenna array approach to
check out not a few thousand but perhaps a few million or even tens
of millions of stars for alien signals. If there were just 10,000
advanced civilizations in the galaxy, they could well strike pay
dirt before Science turns 150.

The technology may well be available in coming decades, but SETI
will also need money.

That's no easy task in a field with as high a
"giggle factor" as SETI has. The U.S. Congress forced NASA to wash
its hands of SETI in 1993 after some congressmen mocked the whole
idea of spending federal money to look for "little green men with
misshapen heads," as one of them put it.

Searching for another tippy-top
branch of the evolutionary tree still isn't part of the NASA vision.
For more than a decade, private funding alone has driven SETI. But
the SETI Institute's planned $35 million array is only a prototype
of the Square Kilometer Array that would put those tens of millions
of stars within reach of SETI workers.

For that, mainstream radio
astronomers will have to be onboard - or we'll be feeling alone in
the universe a long time indeed.

"More than 100 planets have been detected around other stars in the
last 10 years... None of these are thought to support life because
they are [gas giants].... Earth-sized planets have not been
discovered [yet because] it is harder to spot smaller planets - much
harder."

Sean Raymond is a doctoral candidate in astronomy at the University
of Washington, Seattle.

THE SEARCH FOR LIFE outside the Earth is more active than ever as
telescopes probe for intelligent life on other planets while robots
scour the surface of Mars.

There even are desktop computers that
predict which stars might be orbited by Earth-like planets.
Moreover, planets similar to Jupiter are being discovered around
other stars on a monthly basis.

Imagine a planet orbiting a faraway star. It is a bit larger than
Earth and is completely covered by a miles-deep ocean. We think that
such "water world" planets exist around some stars. We also surmise
that there are others with less water, maybe even much drier than
Earth. Can they harbor life? To answer this, we need an
understanding of life here on our own planet.

How and when did life
originate on Earth? Where did Earth come from? Are there "Earths"
orbiting other stars in our galaxy?

Earth formed and resides in the "habitable zone." the distance from
a star at which liquid water may exist on the surface of a planet.
All life on our globe requires some interaction with water. If a
planet is too close to its parent star, like Venus, for example,
water will evaporate from its surface; if it is too far, like Mars,
then water only can exist as ice.

Like Goldilocks' third bowl of
porridge, Earth lies where the temperature is just right. So, the
quest for life on planets around other stars begins as a search in
the habitable zone.

Astronomy has been an active science for thousands of years, and
high-powered telescopes have existed for almost a century. However,
planets around other stars only have been detected in the last
decade. Why can't we just use our big, fancy telescopes to take
pictures of other planets?

Because a planet orbiting another star
appears about 1,000,000,000 times fainter than the star! It is
washed out completely by the light of the star and impossible to
see. It is like trying to hear a whisper from across the stadium
during the Super Bowl.

More than 100 planets have been detected around other stars in the
last 10 years. However, none of these are thought to support life
because they are massive balls of gas hundreds of times as large as
Earth with no surface to stand on! The reason that Earth-sized
planets have not been discovered is that it is harder to spot
smaller planets--much harder. The method used relies on the wobble
of a star as a planet goes around it.

For example, picture a seesaw with a football player on one end and
a kitten on the other: to balance the seesaw, the fulcrum needs to
be placed very close to the football player. The kitten travels way
up and down, but the muscular athlete moves very little. The idea is
the same for a planet orbiting a star. Like the kitten, the planet
is much less massive than the star, and it moves very far compared
with the star.

Yet, like the football player, the star does move,
albeit in a much smaller orbit. The star's wobbling can be detected
with extremely sensitive instruments, and the presence of the planet
can be deduced - remember, we merely can see the light of the star,
not the planet.

It is easier to locate more massive planets since
the star's wobble is greater, just like the football player's motion
is greater if he is balanced by a 10-year-old boy instead of a
kitten.

The wobble of a star due to the orbit of a terrestrial
planet is so small that, employing this method, finding such a
planet is nigh impossible.

New techniques, however, always are on the horizon, and a pair of
upcoming space missions hope to detect a terrestrial planet around
another star: the Europeans are launching Corot in 2006 and NASA is
unleashing Kepler in 2007.

The hope is to uncover planets as small
as a few times the mass of Earth. In addition, the European Space
Agency's Darwin and NASA's Terrestrial Planet Finder missions are
scheduled to launch in the next 10-15 years--with the hope of
finding a few dozen terrestrial planets and probing the composition
of their atmospheres to search for signs of life.

If these missions fail to uncover any signs of life, does that
necessarily mean that Earth is unique, containing the only life in
our galaxy? Absolutely not. These missions merely will be able to
search for planets and life around roughly 50 stars, a tiny subset
of the 100 billion existing in our galaxy. It is like picking one
strand from an enormous haystack, hoping to find the needle.

In this
case, though, we do not know how many needles are in the haystack:
the range is anywhere from zero to millions. It will take decades,
maybe centuries, before we have a clear picture of what the
terrestrial planets in our galaxy look like, and whether there is
life on one or more of them.

Some scientists have approached this dilemma via an alternate route.
Since the formation of the planets in our solar system is relatively
well understood, we can simulate this process in a variety of
conditions in which planets could form around other stars. We can
analyze the bodies that form in these computer simulations to see
how numerous Earth-like planets are, and how often they take shape
in the habitable zone.

In addition, we can attempt to predict
whether habitable terrestrial planets can be created around a star
based on characteristics that can be observed with a telescope.
These predictions can help missions like Terrestrial Planet Finder
to choose their lists of target stars in order to increase the
likelihood of finding potentially habitable planets.

What really makes a planet able to support life?

A planet can form
in the habitable zone and have the necessary temperature for water
to be liquid on its surface, but contain very little or no water.
Having an orbit in the habitable zone is not enough: water is needed
to support life. To better understand this phenomenon, let us look
at how Earth formed and acquired its water.

Earth once was a large disk of dust and gas, slowly accumulating
smaller bodies over a 50,000,000-year span. Each body that impacted
Earth had a slightly different composition, because it formed at a
different distance from the sun at a different temperature. The
boundary separating dry and icy material falls at about 2.5 times
the Earth-sun distance in our solar system, between the orbits of
Mars and Jupiter, and is called the snow line.

Everything formed
inside the snow line was completely dry, but past it are a mixture
of rocks and ice. Since Earth has a lot of water, it must have been
hit by a large number of objects that formed past the snow line and
delivered water to the otherwise dry planet.

Earth mostly is made up
of building blocks that formed in the habitable zone or nearby, but
all of its water came from material forming past the snow line.

Once we understand how Earth acquired its water and became a
habitable planet, we can apply this knowledge to computer models and
test how terrestrial planets form in other environments to see
whether our solar system is the exception or the role.

What these
experiments demonstrate is that the terrestrial planets in our solar
system - Mercury, Venus, Earth, and Mars - are part of a continuum
that can appear in various shapes and sizes.

These simulations of
possible planet systems indicate that every conceivable combination
is out there and probably some we cannot imagine. Some planets in a
star's habitable zone will be dry, but most will contain at least
some water while others may be water-rich. In one simulation, a
planet 3.8 times the mass of the Earth with 40 times as much water
was the only terrestrial planet to form around its star, on an orbit
very similar to that of the Earth around the sun.

The surface of
such a planet would be covered with a global ocean many miles deep
with no land in sight.

The chance that life could exist in such a
place is not well understood because this type of environment is
completely foreign to our solar system, but the possible existence
of these "water worlds" is very exciting, and could provide ideas
for budding science fiction writers.

Planets form in the habitable zone under a variety of conditions.

If
the creation of planets like the Earth can happen in so many
different environments, then it is likely that Earth-like planets
will prove to be relatively common in the galaxy, although it
probably will be a long time before observations can confirm or
reject this.

Phillip: Human language is daunted
by the scale of the cosmic enterprise. Words fail us when we
gaze up at the stars and try to contemplate their significance - and our insignificance.

But there is a word that Iím fond of,
one that attempts to describe the feelings of awe, wonderment,
curiosity and dread that fills us when we look up into the skies
on a clear night. The word is Ďnuminousí. And with the feeling
of the numinous comes another big question.

Are we alone? Are
there other forms of life - particularly of conscious life - out
there? Should we attempt to make contact? How might this be
possible? On the one hand, we acknowledge that the right
conditions to kindle life might be so rare, so fugitive, that
weíre doomed to cosmic solitude. On the other hand, weíre
dealing with such immense numbers of suns and, presumably, of
planets, that life forms may be as bountiful in the cosmos as
they are on Earth.

After all, in the observable universe there
are 1020 - 100 billion billion - suns.

Paul: Thatís a lot, isnít it, a big number. Unfortunately not so
big that if life formed as a result of an accidental shuffling
of molecules - that is, if life is a chemical fluke - then it
would be bound to occur twice.

Phillip: But what if you add to those 100 billion billion suns
the number of possible planets? You are then dealing with an
even greater number.

Paul: Itís just another factor of ten or so. People are very bad
at large number estimates. They think that a million is awfully
big, and a billion just a bit bigger, and so on. Although 100
billion billion sounds like an enormous number, it is still
absolutely tiny compared to the odds against forming life by
random shuffling. It is undeniably true that the universe is
vast: there are a huge number of stars and probably planets too.

Nevertheless the odds against shuffling, say, amino acids into
proteins, which we were talking about previously, are enormous - like one followed by 130 zeros as opposed to your puny number
here of one followed by twenty zeros! A hundred billion billion
doesnít begin to scratch the surface of the improbability of
forming life, if it formed purely by accident.

So if life is
merely a chemical fluke, we are alone. The only possibility of
us not being alone is if there is something other than just a
random shuffling process involved.

E.T. Phone Greece Phillip: There are conflicting human emotions at work here. On
the one hand, it is a very bleak thought, to suppose that we are
alone in the universe. Many of us would like the company of
user-friendly species from other galaxies. On the other hand, we
have always been very arrogant; we rather like to think that we
are at the centre of things.

Paul: In some cultures, yes. But not all. The same argument was
raging even in ancient Greece over 2000 years ago. The Greek
atomists believed that we are not unique. They reasoned that the
universe is nothing but indestructible particles moving in the
void.

This led them to conclude that extraterrestrial beings
exist because if atoms can come together in certain combinations
to form living things here on Earth, then they might do so on
other worlds, too.

Phillip: Does Christianity generally accept the notion that we
are alone?

Paul:Christians have traditionally hated the idea that there
could be intelligent life elsewhere. It causes all sorts of
doctrinal difficulties for them. The problem is not so severe in
other religions, but Christianity has particular difficulty, I
think, with life elsewhere in the universe because Jesus Christ
is traditionally held to be the Savior of mankind only, which
is hard on any alien beings whose ethical or spiritual stature
might dwarf that of humans.

Don't Forget The SunscreenPhillip: Letís reduce the scale from our 100 billion billion
suns. Letís look at our own sun and one of our neighboring
planets - Mars. There has been a lot of speculation about life
on Mars recently.

Paul: Yes, there has. Mars has always been at the forefront of
speculation about life beyond Earth. Remember how 100 years ago
Percival Lowell claimed he saw canals on the surface of Mars? He
believed there were alien beings who built these structures to
bring melt water from the poles to the parched equatorial
regions of the planet.

Then in the 1960s our spacecraft went to
Mars and didnít find any canals, or any other signs of life. For
a while it looked as if Mars was not only red, but dead too.

Paul: Yes, there is the famous Ďface on Marsí too, but weíre not
taking that seriously! The two Viking spacecraft that NASA sent
to Mars in the 1970s were specifically designed to search for
life. They scooped up some topsoil, analyzed it in little
on-board laboratories, and didnít find any compelling evidence
for life - even microbial life.

In fact, the surface of Mars
turned out to be a pretty dreadful place. Itís exceedingly dry,
and very cold - rarely above the melting point of water. On top
of that, it is drenched in deadly ultraviolet radiation, and the
soil is incredibly oxidizing, which is very dangerous to life.
All in all, the surface of Mars is extremely hostile to any form
of life that we know.

Phillip: But Paul, you have established that life occurred on
Earth in extremely inhospitable circumstances.

Paul: That is true, and there has been some speculation that
Antarctica can reproduce conditions not very dissimilar to the
surface of Mars. Remarkably, there are organisms that live in
the dry valleys of Antarctica that I think could live on the
surface of Mars even today, if only they could be shielded from
the ultraviolet radiation.

So, I agree, it is not obvious that
the surface of Mars is completely hostile to life even today.
But nevertheless, itís not a place you would want to be stranded
- Ďnot the kind of place to raise a kidí, as Elton John sang in
ĎRocket Maní.

I think the real reason why Mars looks promising
from the point of view of life is that we know that in the past
it was warm and wet. The photographs of the Martian terrain show
unmistakable signs of river valleys, and there were times when
there was so much water on the surface of Mars there may even
have been an ocean.

Going back about 3.8 billion years, to a
time when we know that there was probably life here on Earth,
Mars wasnít so very dissimilar from Earth. So, I think that
although Mars doesnít look terribly friendly for life today, in
the past it would have been a different story.

The Hitchhiker's Guide For
OrganismsPhillip: Let me return to the matter of the bombardment where
the Earth, our planet, was patinated by large amounts of rubble
being attracted to it. One possibility is that life might have
been introduced to Earth as part of that process.

Given that
rocks have been traded back and forth between the two planets,
could perhaps Earth life have been transmitted to Mars?

Paul: In my mind there is no doubt that if material can travel
between the two planets, then so can organisms. It is entirely
possible that microbes can hitch a ride on a rock and make their
way from Mars to Earth or visa versa.

We know that Mars and
Earth receive hits from time to time with enough force to splash
material into space; at the moment this happens about every few
million years or so, on average.

The ejected debris will be
scattered around the solar system, and some of it will
inevitably be swept up by other planets.

Phillip: So, Paul, all things considered, do you think that
there was life on Mars?

Paul: Iím absolutely convinced that there was, in the remote
past, if for no other reason than it would have got there from
Earth along with the displaced rocks. The bombardment that took
place in the early history of the solar system was so intense
that it would have propelled an enormous number of rocks
backwards and forwards between the two planets.

We know that
Mars was warm and wet at the time there was life on Earth, so I
think it was inevitable that some Earth microbes would have made
their way to Mars inside ejected rocks and found conditions
there rather congenial.

Phillip: But would these little microbes piggybacking on pieces
of rock have made it alive across that distance?

Paul: I agree it does seem extraordinary that even a microbe
could travel through inter-planetary space without being killed,
but when you look at it carefully, it does appear to be
possible. The first hazard is getting blasted off a planet by a
major asteroid or comet impact event. While this looks unlikely,
it actually turns out that an appreciable fraction of rocks can
be flung into space by an impact without being unduly shocked or
compressed.

The Martian meteorites that we have here on Earth,
for example, havenít been pulverized.

I think a microbe could
survive ejection from a planet. It could also survive the
radiation in space because, cocooned inside the rock, it would
be shielded from the worst of the ultraviolet radiation from the
sun, and from the worst of the cosmic rays too. On arrival, a
rock with a suitable trajectory could be braked by air friction
and hit the ground at low speed without burning up.

So, yes, I
think a fraction of microbes could make it unscathed from one
planet to another.

Meteorite From Mars Kills DogPhillip: Conversely could life have begun on Mars and then been
transferred here?

Paul: Absolutely. In fact, I think there is some reason to
favor Mars over Earth for the origin of life. Mars is a smaller
planet, so it would have had less of a bombardment problem. It
would have been possible for microbes to live deeper in the
Martian crust because it wasnít such a hot planet.

Also, it is
easier to blast stuff off Mars because of its lower gravity. So
there is a chance that life began on Mars, maybe as early as 4,
even 4.2, billion years ago, and was subsequently conveyed to
Earth in some of the debris that was splashed off at a later
stage. If that is correct, it leads to the bizarre conclusion
that we are all descended from Martians!

Phillip: How can we be sure that a rock on Earth had a Martian
origin?

Paul: Well, as it happens, the University of Adelaide has been
in possession of a piece of Martian rock for decades, although
nobody realized it until Dr Vic Gostin spotted its significance
a few years ago. It is part of an object that fell in Egypt in
1911 near the town of Nakhla. Incidentally, it killed a dog.

This is the only known example of a canine fatality caused by a
cosmic object! To look at, this Martian meteorite is
unremarkable. Frankly, itís little different from any old bit of
rock that you might find in your garden.

Phillip: We established earlier that physicists, mathematicians
and other members of your profession are regarded as high
priests. I confessed to having a blind faith in your utterances,
but I want you to convince me that there is rock on Earth that
has come from Mars!

Paul: You canít tell by looking at a rock that it has come from
Mars - it is not red or anything. The first clue is that it is a
type of rock called igneous, which means that it was produced by
volcanic activity. Meteorites of the common-or-garden variety
are all bits of debris left over from the formation of the solar
system - primordial and largely unprocessed rocks that were not
accumulated into planets. If something is made by a volcano,
then there is only one place it can have originated, and that is
a planet.

So this rock must have come from a planet. Did it come
from the Earth? Earth has volcanoes. No. How can we be sure?
Because we have got a pretty good understanding of what Earth
rocks are like. When you study the chemistry of this rock, you
find that it is subtly different from any rocks on Earth. In
particular, the oxygen isotopes in rocks from Mars have
different ratios from Earth rocks and, incidentally, from moon
rocks.

Phillip: So it has a Martian fingerprint all over it.

Paul: At least a non-terrestrial fingerprint. So, we are looking
for a planet in the solar system, other than Earth or its moon,
with volcanoes.

Mars is the obvious answer. Look at the pictures
of Mars - it has some of the biggest volcanoes in the solar
system. Itís a volcanic planet. However, even that is not the
clincher. It turns out that the best evidence we have that
meteorites come from Mars - and there are about a dozen of them
that have been collected so far - is that trapped within the
rock are gases from the Martian atmosphere.

In the 1970s the
Viking spacecraft, which landed on the surface of Mars, measured
the different isotopes of the gases - argon, xenon and so on - in the thin Martian air.

Those isotope ratios match exactly the
isotope contents of our Martian rocks. That is just too much to
be a coincidence, so they clearly do come from Mars. I donít
think many scientists now seriously doubt that.

The Secret Life of ALH84001Phillip: Do any of our Earth-bound meteorites contain hints of
life?

Paul: Yes, a meteorite found in Antarctica in 1984, code-named
ALH84001, contains tantalizing evidence for life. Indeed, there
are some scientists at NASA who are convinced that life has been
at work in that meteorite. There are three reasons why the NASA
scientists are excited by it. One is that it contains tiny
grains of carbonate - and to a geologist carbonate suggests one
thing: water.

Of course, all life as we know it depends on
water. If you look very carefully with a microscope at these
carbonate grains, there are other features, little mineral
inclusions within them, which suggest that some sort of organic
processing has gone on. If you saw such features in an Earth
rock you would attribute them to bacterial activity.

Phillip: It wouldnít be a line call? You would be absolutely
confident that it was bacterial activity?

Paul: It would be pretty certain if it was in an Earth rock,
yes. But of course if you see it in a Mars rock, you think
again. However, the mineral grains were not all.

The scientists
from NASA also found ring-shaped organic molecules known as PAHs
which living organisms can produce. Unfortunately PAHs can also
be made by normal chemical means, so it is not conclusive
evidence for life.

The third line of evidence, and I suppose the
thing which most captured the public attention when the results
were announced, was the existence of tiny little sausage-shaped
features, little microscopic blobs, reminiscent of fossilized
bacteria. Nobodyís claiming they are living bacteria, but they
could be bacterial fossils. All these findings have been
disputed - the jury is still out on them.

Phillip: How old would these putative fossils be?

Paul: The figureís a bit rubbery, but 3.6 billion years seems a
good estimate. These could be very ancient Martian microbes.

Phillip: And what prospects are there for life on Mars today?

Paul: As we discussed earlier, the surface of Mars is not very
promising for life. However, deep underground, where the
permafrost is melted by geothermal heat, conditions may well
resemble those beneath the surface of the Earth, a region we
know is seething with microbial life. My personal belief is that
there probably is microscopic life in the subsurface zone on
Mars even today.

Phillip: Okay, letís take the optimistic view that yes, life did
exist on Mars, and may even exist on Mars today. If that is the
case we can extrapolate to the wider universe. The probability
is that many of the billions of stars we have mentioned have
planets. Do you take the view therefore, that life is likely to
be bubbling away all over the cosmos?

Paul: Because
we are almost completely ignorant of how life
began, that is an open question. Personally I would say that
life is common throughout the universe, but I am arriving at
that point of view largely on philosophical rather than
scientific grounds.

Phillip: Philosophical? In what sense?

Paul: I donít believe that we are freaks, that life on Earth is
the result of a single stupendous, meaningless accident. I think
that life is part of the natural outworking of the underlying
laws of physics, laws that govern a bio-friendly universe.

Emotional IntelligencePhillip: Is that an emotional need of yours?

Paul: Probably, yes. Iím coming at this entirely from the
philosophical, or, if you like, emotional direction. Not from a
scientific direction, because the scientific evidence is very
equivocal. We donít know how life began. We have no idea whether
it was a unique event or whether it is something that occurs
easily under the right conditions.

I might say that many
scientists are biological determinists: they think that it is
rather easy for life to form under the right conditions.

They
also point out the fact that the basic building blocks of life,
the amino acids and so on, are very common throughout the
universe, and that the stuff of which life is made - the basic
elements like carbon, nitrogen, oxygen, hydrogen and so on - are
among the most abundant elements in the universe.

Therefore they
conclude that life is likely to be abundant in the universe, but
we donít know that. It is pure conjecture.

Phillip: If there is a miracle - and as an atheist I find that
an embarrassing word to use - but if there is a miracle in the
story of life, I find it in the growth or the development of
consciousness: self-regarding, self-aware consciousness. Is
there in your view a likelihood that consciousness would develop
in other realms on other planets? Is that a part of the
inevitability, the coding?

Paul: If we accept
Darwinís theory of evolution as a complete
picture of the evolutionary changes that have taken place among
life on Earth, then it would seem extremely unlikely that
consciousness would develop anywhere else.

Consciousness would
simply be a quirky little by-product of the blind groping of
evolution, in the same way that fingernails and eyebrows and so
on have appeared. In other words, they donít have any deep
significance.

Phillip: Some quirk.

Paul: Naturally we regard it as immensely significant because we
are the products of it. However, there is no known law that
operates in evolution to direct the evolutionary change towards
consciousness or intelligence. If evolution is blind, if it is
just a random groping through the space of possibilities, then
the chances of Earthís evolutionary pathway being paralleled on
another planet are infinitesimal.

Of course, if there is more to
it than Ďblind watchmakerí Darwinism, then this conclusion may
be wrong. Consciousness and intelligence may emerge as a natural
by-product of bio-friendly laws. We donít know, but it is
important to put the matter to the test.

Phillip: By test, you mean SETI - the search for
extraterrestrial intelligence - using radio telescopes to seek
out signals from alien civilizations? Given your optimistic
philosophy, do you regard SETI as a worthwhile project?

Paul: When people ask me about SETI I say that it is almost
certainly a hopeless enterprise, just because of the enormous
odds against locating an alien intelligence even if the universe
is full of them. Still, itís a glorious enterprise nonetheless,
and well worth doing. I am a thorough supporter of SETI. Alas,
though, the chances of success are extremely small.

Of course, such visits are
passionately believed in by many, many people, most of whom live
in California! What in your view is the likelihood of successful
space travel.

Paul: Suppose we do live in a universe in which not only life is
inevitable, but conscious, intelligent life, too. Suppose
furthermore that some fraction of intelligent life develops into
technological communities.

You might then conclude that the
Earth should have been visited, and might still be visited
today, by alien creatures. It is an argument, incidentally,
often used in support of the contrary belief, that life is
unique to Earth - the Ďwhere-are-they?í argument. If the
universe was teeming with life we ought to see evidence of these
alien beings, and as we donít, therefore we must be alone.

My
feeling about this is that if life does develop to the point of
technology, it makes no sense at all to travel in the flesh from
one star system to another. It is immensely expensive. It is one
thing to travel from planet to planet within a given star system
- we will be able to do that soon - but traveling between star
systems is quite another thing.

The distances are so immense:
the nearest star is 4 1/3 light years away from Earth.

Phillip: Turn it into kilometers or miles.

Paul: A light year is about ten trillion kilometers or six
trillion miles. To put that into comparison, light takes a
second or so to reach Earth from the moon, and about 8 1/2
minutes to reach us from the sun, which is a 150 million
kilometers away.

Weíre talking 4 1/3 years to the nearest star.
Now if the universe is teeming with life, as some people
suggest, and if there are many, many technological communities
out there, physical space travel would be a poor way to make
contact.

It would make much more sense for an alien
civilization
to log onto the nearest node of the galactic internet and upload
the video of their planet to their friendly alien neighbors
next door, than to literally travel there in the flesh. The cost
of interstellar travel is so horrendous that it makes no
ecological or economic sense to do it.

If thereís an intelligent
community out there that can communicate, we could contact them
much, much less expensively by radio or laser once we know where
they are located.

Phillip: Then, of course, there is the problem of the timing.
Our planet has existed for four billion years, while something
approaching the human being has been around for a mere four
million years.

And that human being has been capable of sending
radio signals for only about four decades. So you would need
some amazing synchronicities to be occurring.

Paul: Thatís absolutely right. A lot of people have an image of
alien beings that are only a few decades ahead of us
technologically.

They donít realize how improbable this is. As
you point out, life on Earth has taken about four billion years
to evolve to the point of technological society. Now supposing,
hypothetically, there was another planet out there where life
got going at exactly the same time as it did here on Earth.

There have been so many accidents of evolution, so many little
byways in the evolutionary process, that the chances of the same
sequence happening on another planet, reaching the same point of
development to within 100 years or so of us is infinitesimal.

That is why I donít believe the UFO stories because the reported
aliens are just too much like us, not only in bodily form, but
in their level of technology. If you read the reports, UFOs seem
to be something like the next generation of stealth bombers!
Just 100 or 200 years ahead of us technologically.

The chances
that any two planets would arrive at that similar level of
technology after four billion years of evolution are simply
infinitesimal. Then take into account the fact that there have
been stars around for billions of years before our solar system
even formed. There could be planets - and indeed life forms - that stretch back for many more billions of years than life on
Earth.

The conclusion you arrive at is if there are other
intelligent beings out there, they will either be way, way ahead
of us technologically, or way, way behind. If the latter is the
case, they wonít be signaling us across interstellar space. So
if we do succeed at SETI and pick up an alien signal, it is
likely to be from a civilization enormously more advanced than
ours.

Phillip: Previously, I quoted Asimov's term Ďthe armies of the
nightí, which he used to describe the serried ranks of those
opposed to science. You might also argue that the term could be
applied to believers in the UFO phenomenon, although in this
case the armies of the night are people with a passionate love
of science.

They love science to such excess it would seem that
they have turned the UFO into a sort of twentieth-century
religion. There is a paradox here.

Paul: I think that the UFO scene really is religion with a thin
veneer of science. What is happening is that old fairy stories
or Bible stories of religious visitation have been overlaid with
technological language. I was always impressed by Ezekielís
vision of four flying wheels, full of eyes, out of which stepped
an angel with the likeness of a man.

Replace Ďwheelí by disc,
Ďeyesí by portholes, and Ďangelí by Ufonaut, and you have a
classic flying saucer story!

Virtual RealityPhillip: Americaís energetic pop culture has given us a series
of fads. Thereís been the yo-yo, the frisbee, the hula hoop and
the flying saucer - all things, I point out, that spin.

Now the
latest phenomenon is, of course, the bodily abduction, as big a
fad as the yo-yo. I was recently alarmed when I met and talked
with a professor from Harvard whoís a passionate believer in
bodily abductions, having interviewed, he says, simply hundreds
of abductees. Your view on this please.

Paul: I have my own theory about alien abductions. It may not
explain all of the cases, but I think it explains some. The
abduction stories have many features in common with a phenomenon
known as lucid dreaming. Iím not talking about vivid dreams; we
all have vivid dreams. Thereís another type of dream state,
quite different, which most people will have spontaneously
perhaps only once or twice in their lifetime. I have certainly
had lucid dreams.

How do they differ from ordinary ones? In a
normal dream everything has a sort of wishy-washy quality.

By
contrast, in a lucid dream things take on a type of reality
which is every bit as sharp and real as you and me sitting here
now. If you are not aware that you are having a lucid dream - these days I always am, but if you didnít know it
- it could be
quite terrifying. A well-known feature of the normal dream state
is a sense of paralysis.

Weíve all had that dream where we are
trying unsuccessfully to run away from things. If you get that
feeling in a lucid dream it can be really very scary - I have
had the experience myself.

Another prominent dream image is
levitation, a sense of floating or flying. Again, it can occur
in the lucid dream state, too. There can also be a strong sense
of a malevolent presence.

When I have a lucid dream, I usually
think that somebody has broken into the house, and they are in
the room, standing at the end of the bed.

Phillip: So you are suggesting that these dreams can be
conflated with reality?

Paul: Well, you see, if you put all those elements together you
have many of the aspects of alien abduction. Somebody falls
asleep, in the middle of the night they have a sense of a
malevolent presence nearby, they are paralyzed, and find
themselves floating.

The other distinctive feature of lucid
dreams is that you have a strong sense of touch. Again, in the
lucid dreams Iíve had, it is usually a feeling of something
prodding or poking me.

When I was a child and would have these
dreams, I thought the cat was walking over me.

The Intergalactic ShortcutPhillip: Okay, I can accept that, particularly if the dreams are
then to some extent choreographed by a mass media or given a
form and structure. Now I would be remiss if I didnít ask you a
final question, and that is the wormhole argument.

The late
astronomer Carl Sagan suggested that it may be possible for
interplanetary, intergalactic, cosmic visitations to occur
through the wormhole. Your response?

Paul: It is quite interesting, historically, what happened here.
Carl Sagan wrote the book
Contact, now a movie starring Jodie
Foster. It features a so-called wormhole as an imaginary mode of
faster-than-light space travel.

When Sagan finished the book he
went to his friend Kip Thorne at Caltech to discover if rapid
transit through a wormhole could really be done.

So there began
a sort of recreational mathematical exercise to see if it was
possible to have a shortcut between two points in space that
would enable rapid transportation from one place to the other.
It is already known that black holes can do funny things to
space and time, and Saganís hypothetical wormhole is somewhat
like an adaptation of a black hole.

As a result of these
theoretical studies, Thorne and his colleagues decided that it
was just about feasible - not a very practical proposition - but
just about feasible that you could have such a wormhole.

But
there was a bizarre twist to this conclusion. It turned out that
if you could go through the wormhole and come out the other end
a short time later, maybe only a few minutes later, then the
wormhole could also be used as a time machine, it could send you
back in time!

So most of the theoretical work that has since
been done involves looking at mathematical models of wormholes
in the context of
time travel rather than space travel.

However,
it does look like it is theoretically possible to create a
wormhole and use it for space travel, but it would certainly be
a very expensive exercise.

We have no hard evidence at this time that there is life to be found
anywhere else in either our solar system, or the rest of the
universe.

Still, as an astronomer, I think the chances are very good
that life exists elsewhere.

Paleobiologists report that life on this planet may have arisen not
once but several times when the Earth was very young, perhaps only a
few hundred million years old. During this period, there were many
frequent impacts with very large asteroids as the formation of the
Earth was ending or the Moon was being formed, and each of these
impacts would have incinerated any biological system then in
existence.

The planet Mars very likely had lots of running water on its surface
when it was very young, but lost it all once the atmosphere leaked
away. But there could have been a period lasting over one billion
years when bacteria like that on Earth could have formed. That's why
we are now excited about looking for fossils of ancient martian
bacteria on Mars.

If we find them, that will mean that the
conditions for evolving life, even just bacteria to start with, are
fairly generous and we could expect lots of bacterial life in the
universe given that a planet orbits its star at the right range of
distances.

We now know that our solar system was formed in a way that is common
to many stars. We have observed disks of matter orbiting young
stars, and even old ones, that is probably dust and asteroidal
material. We have even detected signs of planets orbiting several
stars, though additional work is needed to firm up this as the only
explanation for the data we have.

So, I think the chances are better than ever that there is life
elsewhere in the universe.

We still don't know how often evolution
ends up with intelligent beings. This may be very rare considering
the fickle conditions that had to occur on Earth for mammals and
intelligence to become an important evolutionary skill.

Dumb animals
lasted billions of years on this planet before something like homo
sapiens evolved!

A universe filled with bacteria and dinosaurs could
be the rule, not the exception.